7 Expressions [expr]

7.6 Compound expressions [expr.compound]

7.6.1 Postfix expressions [expr.post]

7.6.1.8 Type identification [expr.typeid]

1
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The result of a typeid expression is an lvalue of static type const std​::​type_info ([type.info]) and dynamic type const std​::​type_info or const name where name is an implementation-defined class publicly derived from std​::​type_info which preserves the behavior described in [type.info].54
The lifetime of the object referred to by the lvalue extends to the end of the program.
Whether or not the destructor is called for the std​::​type_info object at the end of the program is unspecified.
2
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If the type of the expression or type-id operand is a (possibly cv-qualified) class type or a reference to (possibly cv-qualified) class type, that class shall be completely defined.
3
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When typeid is applied to a glvalue whose type is a polymorphic class type ([class.virtual]), the result refers to a std​::​type_info object representing the type of the most derived object ([intro.object]) (that is, the dynamic type) to which the glvalue refers.
If the glvalue is obtained by applying the unary * operator to a pointer55 and the pointer is a null pointer value ([basic.compound]), the typeid expression throws an exception ([except.throw]) of a type that would match a handler of type std​::​bad_typeid exception ([bad.typeid]).
4
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When typeid is applied to an expression other than a glvalue of a polymorphic class type, the result refers to a std​::​type_info object representing the static type of the expression.
Lvalue-to-rvalue, array-to-pointer, and function-to-pointer conversions are not applied to the expression.
If the expression is a prvalue, the temporary materialization conversion is applied.
The expression is an unevaluated operand.
5
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When typeid is applied to a type-id, the result refers to a std​::​type_info object representing the type of the type-id.
If the type of the type-id is a reference to a possibly cv-qualified type, the result of the typeid expression refers to a std​::​type_info object representing the cv-unqualified referenced type.
[Note 1: 
The type-id cannot denote a function type with a cv-qualifier-seq or a ref-qualifier ([dcl.fct]).
— end note]
6
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If the type of the expression or type-id is a cv-qualified type, the result of the typeid expression refers to a std​::​type_info object representing the cv-unqualified type.
[Example 1: class D { /* ... */ }; D d1; const D d2; typeid(d1) == typeid(d2); // yields true typeid(D) == typeid(const D); // yields true typeid(D) == typeid(d2); // yields true typeid(D) == typeid(const D&); // yields true — end example]
7
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The type std​::​type_info ([type.info]) is not predefined; if a standard library declaration ([typeinfo.syn], [std.modules]) of std​::​type_info does not precede ([basic.lookup.general]) a typeid expression, the program is ill-formed.
8
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[Note 2: 
Subclause [class.cdtor] describes the behavior of typeid applied to an object under construction or destruction.
— end note]
54)54)
The recommended name for such a class is extended_type_info.
55)55)
If p is an expression of pointer type, then *p, (*p), *(p), ((*p)), *((p)), and so on all meet this requirement.